Algae fills a pool fed by Canada Glacier in the Dry Valleys region of Antarctica. With some experts forecasting the melting of half the Arctics summer sea ice by the centurys end, scientists are becoming increasingly concerned about the state of the Earths natural air conditioner.

If Greenlands massive ice sheets were to melt, something that could occur over the very long term, they could raise the sea level by 23 feet (7 meters).